US-backed Syrian forces say they captured 41 positions held by Islamic State of Iraq and the Levant (ISIL, ISIS) and destroyed fortifications in a fierce battle to capture the armed group’s last enclave in eastern Syria.

Military advances were made overnight and on Sunday as the Kurdish-led Syrian Democratic Forces (SDF) launched a final push to clear the area from ISIL fighters after 20,000 civilians were evacuated from the area in Deir Az Zor province, said Mustafa Bali, a SDF spokesman.

Bali said heavy fighting was ongoing inside the village of Baghouz on Sunday. He did not say how long the battle was expected to last.

“The clashes are ferocious naturally because the terrorist group is defending its last stronghold,” he said.

The group overran large parts of the country and neighbouring Iraq in 2014, but various military offensives have since reduced that territory to a patch on the Iraqi border.

The SDF, supported by a US-led coalition, announced a final push to retake the pocket in the village of Baghouz late on Saturday.

An estimated 600 ISIL combatants, most of them foreigners, remain in the area and are apparently willing to fight to the death. Between 500 to 1,000 civilians are also estimated to be inside, Bali said.

“If we can, in a short timeframe, get the [remaining] civilians out or isolate them, I believe that the coming few days will witness the military end of the terrorist organisation in this area,” he added.

Al Jazeera’s Imran Khan, reporting from Gaziantep on Turkey’s border, said ISIL fought back against the onslaught with improvised explosive devices.

Final battle

The Syrian Observatory for Human Rights (SOHR), a UK-based war monitor, said coalition planes and artillery bombarded ISIL positions.

“The battle is ongoing. There were heavy clashes this morning, with landmines going off,” said SOHR’s head Rami Abdel Rahman.

Backed by US-led coalition air strikes, the Kurdish-Arab alliance has in recent months cornered the remaining ISIL fighters in a final patch of territory in Deir Az Zor.

The alliance has since whittled down the ISIL-held territory to a scrap of just 4sq km on the eastern banks of the Euphrates.

US President Donald Trump predicted that ISIL will lose the territory it once controlled in Iraq and Syria this week.

US withdrawal

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The group, however, retains a presence in Syria’s vast Badia desert, and has claimed a series of deadly attacks by sleeper cells in SDF-held areas.

In December, Trump announced the withdrawal of 2,000 US troops from Syria in a surprise move, saying the ISIL had been defeated.

A top US general said last week ISIL will pose an enduring threat following the US withdrawal as it still has leaders, fighters, facilitators and resources.

Syria’s Kurds have largely stayed out of the country’s civil war, instead building semi-autonomous institutions in northern and northeastern regions they control.

Spearheaded by the Kurdish People’s Protection Units (YPG) militia, the SDF has been the main US ally in Syria.